Polyurethanes are one of the most versatile class of polymeric materials. They are particularly useful in rigid and flexible foams. Flexible polyurethane foams are used as cushioning for a variety of consumer and commercial products, including bedding, furniture, automotive interiors, carpet underlay and packaging. Rigid polyurethane and polyisocyanurate (polyiso) foams create one of the world's most popular, energy-efficient and versatile insulations. Environmental health and safety, along with fire protection, are driving change within the insulation industry. The high thermal insulation of rigid polyurethane makes them the most suited and efficient technologies to address these needs. These global trends drives demand for continuous innovation across the polyurethane industry.
Polyurethane foams are produced by reacting an isocyanate with a polyol. The polyol component is typically one or more polyols along with a surfactant, catalyst, fire retardant and a blowing agent to make a foam. The most common polyols used in the industry are polyether polyols and polyester polyols. Each of these class of compounds have their own merits and demerits. Polyether polyols provides hydrolytic stability, lower viscosity and flexibility. Aromatic polyester are known to contribute to flame retardance and higher modulus. However, they are typically limited in functionality and inherently, higher in viscosity and hence formulations especially in rigid PU systems have to use a co-polyol such as polyether polyols with higher functionality. Furthermore, sugar-based polyols that are one of the most commonly used co-polyol in these formulations do not offer any burn resistance.
Alkoxylated phenol-aldehyde resins have been found to be useful in the preparation of various polymeric products including polyurethane compositions and foamed products. These are typically called novolac based polyether polyols. They are prepared by reacting novolacs with alkylene oxides. These types of polyols have the advantage of having a high aromatic content which is known in the industry to aid in improved reaction to fire and can have high functionality. However, formulators still need to use other polyols along with amine-based catalysts and fire retardants to achieve the desired thermal, fire and mechanical performance.
The Spray Polyurethane Foam (SPF) market, for example, is one of the fastest growing polyurethane segments due to the superior ability of SPF to provide high insulation, reduce noise and for the ability to retrofit existing buildings and infrastructure. However, many SPF formulations utilize small molecule organic and inorganic catalysts to provide quick reaction and phosphate or phosphate-chlorinated additives in order to function and meet building regulations for fire ratings. Small molecule catalysts such as amines can be volatilized during spray polyurethane installation that poses health hazard. Small molecule fire retardants that are invariably added to these formulations, are under regulatory scrutiny for concerns related to their effect on the environment.
Thus, there is an increasing demand for better performing rigid polyurethane foams that have particular flammability specifications and acceptable physical properties. There exists a need in the industry for a polyol with high reactivity towards isocyanate, inherent flame resistance, high functionality to achieve the desired properties and to allow reduction or elimination of the volatile amine-based catalysts and small molecule flame retardants.